There are many applications wherein it is desirable to cause circulation within a body of fluid. Common reasons for providing circulation are for mixing, to prevent stratification and to aerate a body of liquid. Examples of these will be discussed later within this specification.
A large number of methods have been devised to cause the desired circulation. In one example, in the case of liquids, it is common to hold the liquid body within a cylindrical tank having its central axis oriented vertically and to cause the liquid to be moved within the tank by the action of an impeller driven by a motor. Many other means have been devised to cause the body of liquid to rotate. Nevertheless, these techniques require the expenditure of significant energy and often give rise to associated problems. Many of these inefficiencies and problems arise because such systems have not been designed to cause the fluid to be circulated in accordance with the natural flow tendencies found in nature.
In nature, fluid flow is essentially turbulent or vortical. A vortex ring cross-sectionally rolls, much like a wheel, rather than slides. Famed hydrodynamisist, Reynolds once stated, in reference to ring vortices, that “Nature prefers to roll rather than glide”.
It is this feature that greatly contributes to ring vortex efficiency.